# Chapter 2: Earth Structure

## Law of Conservation of Matter

• Matter cannot be created or destroyed
• Can be transformed from one substance to another

Matter- All the material in the universe that has mass and occupies space, whether solid, liquid, or gaseous

• All matter is composed of elements

Element - A fundamental type of matter, a chemical substance with a given set of properties, that cant be be broken down into substances with other properties.

• Composed of atoms, the smallest components that maintain the chemical properties of that element.

## Atomic Structure

• Every atom has a nucleus consisting of protons and neutrons.
• The atoms of each element have a defined number of protons in its nucleus
• Atoms of the same element with differing numbers of neutrons are called isotopes
• Radio-Isotopes - Decay at a rate determined by its half life, the amount of time it takes for half of the atoms to give off radiation and decay.
• Atoms also may gain or lose electrons form their outer shells, they become ions, electrically charged atoms or combination of atoms.
• Ions are denoted by their elemental symbol followed by their ionic charge.
• Ions that form when an atom loses electrons ﻿$\rightarrow$﻿ Carry a positive charge ﻿$\rightarrow$﻿ Cations
• Ions that form when an atom gains electrons ﻿$\rightarrow$﻿ Negative charge ﻿$\rightarrow$﻿ Anions
• Atoms can link chemically to form molecules, combinations of two or more atoms
• A molecule composed of atoms of two or more different elements is called a compound.
• Eg, Water
• Atoms bond, or combine chemically, because of an attraction one another’s electrons.
• When atoms in a molecule share electrons, they generate a covalent bond.
• A mixture of two or more substances is called a solution.
• In any aqueous solution, a small number of water molecules dissociate, each forming a hydrogen ion and a hydroxide ion (OH-)
• Organic Compounds - Consist of carbon atoms joined by covalent bonds, often with other elements such as nitrogen, oxygen, sulphur and phosphorus
• Inorganic Compounds – Water is an example

## Ecology

• Autotrophs - Also known as primary producers, include green plants, algae and cyanobacteria.
• Photoautotrophs - Turn light energy from the Sun into chemical energy via photosynthesis

### Photosynthesis

In photosynthesis, sunlight powers a series of chemical reactions that convert carbon dioxide and water into sugars, transforming low-quality energy from the sun into high quality energy the organism can use.

• Animals survive by being consumers, or heterotrophs, organisms that gain their energy by feeding on other organisms.
• They eat plants hence they become primary consumers, or they eat animals that have eaten plants and become secondary consumers.
• Utilizing the chemical energy created during photosynthesis requires a process called cellular respiration.
• To release the chemical energy of glucose, cells use the reactivity of oxygen to convert glucose back into its original starting materials: Respiration
• It oxidizes glucose to produce carbon dioxide and water
• The equation is the complete opposite of photosynthesis

Geothermal Energy - Is heat that emanates from earths interior

• Powered primarily by radio activity
• Radiation from naturally occurring radioisotopes deep inside Earth heats the inside of the planet, and this heat gradually makes its way to the surface

Chemosynthesis - Is the process of transforming inorganic carbon into organic carbon compounds

## Layers of Earth

Core - Consists mostly of iron, solid in the inner core and molten in the outer core

Asthenosphere - A portion of the upper mantle

Mantle - Surrounds the core and is a thick layer of rock

Lithosphere - The harder rock above the asthenosphere

Crust - The lithosphere includes the uppermost mantle and the crust, it is thin, brittle, low density layer of rock that covers he Earths surface.

### The Core

• Inner Core ﻿$\rightarrow$﻿ Solid
• Outer Core ﻿$\rightarrow$﻿ Liquid
• “The peach analogy”

### The Mantle

• Made of relatively dense rock
1. Not as dense as the core
• Asthenosphere
1. “Weak Zone”
2. Near melting point

### The Crust

• Basalt
• Dense, thin

#### Continental Crust

• Granite
• Less dense, thick

Crust ﻿$+$﻿ Top of Mantle ﻿$=$﻿ Lithosphere

### Mantle Convection

• Plate tectonics happen due to mantle convection
• Convection - magma causes crust to move
• Mantle convection drives plate motion
• Hot rock (low density) rises from depth and cool rock density) sinks from the surface
• Hot, mobile mantle + thin, cool, brittle, lithosphere -> breaks into plates

Intraplate - “Middle” of the plate - center

#### Plate boundaries

• Divergent (plates moving apart)
• Convergent (plates moving together)
• Transform (plates moving horizontally past)

Intraplate - Geologically quiet with some exceptions.

• Hot spots” e.g. Hawaii

Divergent - New crust is generated

• Oceanic (ex. mid-Atlantic Ridge)
• Continental (ex. East African Rift)

### Convergent Plate Boundaries

• Crust is consumed or compressed
• Ocean-ocean – one of the crust of the ocean goes underneath - subduction zone (ex. Japan)
• Ocean-continent subduction zone (ex. Andes): Ocean will go down again
• Continent-continent collision zone (ex. Himalayas)

### Transform Plate Boundaries

• Crust is neither created nor destroyed eg. San Andreas Fault

### Internal processes, in turn, directly influence:

• Composition of the atmosphere
• Typography and landscape
• Climate, weather, soil, biomes

• A system is a portion of the universe that can be separated from the rest, for the purpose of studying changes that occur within it, under changing conditions.
• Environmental entities are complex systems that interact with each other.
• Network of relationships among components that interact with and influence one another.

### Major earth spheres

• Geosphere
• Atmosphere
• Hydrosphere
• Biosphere

Boundaries overlap, systems and systems and subsystems interact.

### Types of Systems

Based on properties of boundaries

Closed System - Energy can be exchanged across the boundaries, but matter cannot.

Open System - Both matter and energy can be exchanged across the boundaries

• Earth is a closed system, but everything inside is an open system
• We cant get new resources
• Example of open system: bake a pie, seal tight oven. Scent is coming out.
• Earth itself approximates a closed system.
• Living in a closed system has some consequences
• Resources are finite and limited.
• There is no “away” to throw things to.
• “What goes around comes around”

Dynamic Equilibrium - Systems are constantly changing, interacting, balancing.

Homeostasis - many systems tend to maintain stable internal conditions (=Resistance)

Resilience - Some systems (not all) recover easily from disturbances

Emergent Properties - System characteristics not evident in individual components on their own

### Emergent Properties

• System characteristics not evident in individual components on their own.
• The whole is more than the sum of the parts.
• A cycle is a system of two or more connected reservoirs, in which material (or energy) is transferred in a cyclical fashion.
• A way of understanding and modelling where substances come from, where they go, where they “reside” in the Earth system, and how they are transferred and transformed.

Matter and energy in systems and cycles obey the rules of thermodynamics but they behave somewhat differently:

• Matter is recycled through environmental systems, changing form as it goes.
• Energy comes into the Earth system, flows through, is used and degraded, and then exits the system.
• Energy cannot be created or destroyed but it can be degraded and transformed.

### Reservoirs

#### Physical boundaries

1. The ocean
2. An organism
3. A magma chamber under a volcano

#### Contents (a “mass” of material)

1. Ozone in the stratosphere
2. Fish in the ocean
3. Mercury in ocean fish

When we portray the characteristics and functioning of a cycle or any other environmental process, its called a model.

#### Models of natural cycles & other processes can be

• Physical models
• Landscape drawings
• Box models
• Mathematical models

#### Box models typically give quantitative information about:

• Reservoirs (boxes)
• Contents (number in the boxes)
• Transfer processes (arrow)
• Fluxes (number on the arrows)

Box modes are the first step in developing mathematical and computer models… each process is flux

Content (or burden) of a reservoir

﻿$=$﻿ Total mass of a substance in the reservoir

﻿$=$﻿ Concentration ﻿$\times$﻿ Mass of physical unit

Example ﻿$\rightarrow$﻿ Content of sodium in seawater

﻿$10.78$﻿ g/kg (salinity of seawater) ﻿$\times1.4 \cdot 10 ^ {21}$﻿ kg (total mass of of the ocean)

﻿$= 15.1 \cdot 10 ^{21}$﻿ g

﻿$=$﻿ burden of Na

### Transfer Processes

• Mechanisms that cause substances to move from one reservoir to another
• Physical, chemical, biological or a combination

Examples

• Hydrologic Cycle ﻿$\rightarrow$﻿ Precipitation, runoff etc
• Rock Cycle ﻿$\rightarrow$﻿ Erosion, sedimentation etc
• Sodium Cycle ﻿$\rightarrow$﻿ Sea spray etc.

Flux - Amount of material transferred, described in terms of mass or volume per unit of time.

• Fluxes are controlled by rates of transfer processes and capacities of reservoirs.
• Source - where the flux is coming from
• Gives out more than it takes in

Sink - Where the flux is going

• Takes in more than it gives out
• If sources ﻿$=$﻿ Sinks ﻿$\Rightarrow$﻿ Steady State

Positive Feedback - Self-reinforcing, self perpetuating” cycle

Negative Feedback - Self-regulating, self-limiting. Homeostatic cycle

Positive Feedback Loop - Output from the system acts an input that drives the system farther in the same direction – toward one extreme or another

Negative Feedback Loop - Output from the system acts an input that moves the system in the opposite direction – Stabilizing it or returning it to the starting point.

### Geological Cycles

#### Rock Cycles

• Heating, melting, cooling, breaking, reassembling of rocks and minerals.
• Dominated by surface process

#### Tectonic cycle

• Processes related to the movement of large fragments of lithosphere
• Dominated by internal processes

#### Geological Cycles

• Determine soil chemistry and replenish nutrients
• Drive formation of mineral resources and fossil fuels
• Influence development of landscapes and mountain ranges
• Contribute to changes in atmospheric chemistry
• Determine location, size, and shape of ocean basins

• Igneous
• Metamorphic
• Sedimentary

### Igneous Rock

Magma - Molten (liquid) rock ﻿$+$﻿ gases ﻿$+$﻿ crystals

Lava - Magma that reaches the surface

Igneous Rock - Forms when magma cools

• Intrusive (plutonic) rock
• Magma cools and crystallizes slowly, well below Earths surface (eg. granite)
• Extrusive (volcanic) rock
• Magma ejected from a volcano, cools and solidifies quickly (eg. Basalt)

### Sedimentary Rock

Sediment - Particles of rock, transported by wind, water, ice or gravity

Sedimentary Rock - Forms in the near surface or surface environment

Lithification - Formation of rock through the processes of compaction and cementation

Fossils - Preserved remains of long dead organisms.

Metamorphic Rocks - Pre-existing rock modified as a result of exposure to great heat and/or pressure

• Temperature and pressure high enough to reshape crystals
• Changes their appearance, physical properties, even their chemistry.

### Earth is not homogeneous

#### Internal layering is defined by

• Differences in physical properties
• Differences in composition

#### Direct study of rocks

• Surface rocks
• Drill holes
• Lava
• Xenolith - “Foreign rocks”

#### Indirect methods

• Astronomical & orbital measurements
• Planetary mass and density
• Meteorite analogy
• Planetary composition
• Gravity & magnetism measurements
• Refraction of seismic waves

Earthquakes occur as a result of the build up and release of strain energy in blocks of rock subjected to tectonic forces.

## Earthquakes

Ground shaking that accompanies the release of energy caused by fracturing of rocks, due to the strain energy that builds up as a result of a plate motion.

Fault - rock fracture along which relative movement occurs

Focus - initial point of rupture along a fault

• Focal depth influences earthquake impacts

Epicentre - point on the surface directly above the focus

• Seismic waves are refracted if they travel more quickly through some layers than through other layers.
• Seismic waves are blocked by the outer core because they can’t travel through liquids.
• Travel paths of seismic waves are the single most important source of information about Earths interior.